Section 03 - Compressor Basics
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Transcript of Section 03 - Compressor Basics
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7/28/2019 Section 03 - Compressor Basics
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Compressor basics
Siemens AG 2007. All rights reserved.Page 1
COMPRESSORS
SCREWRECIPROCATING CENTRIFUGAL AXIAL
STATIC DYNAMIC
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Compressor selection Compressors
Reciprocating
compressors
Rotary vane
compressors
Screw compressors
m
Centrifugal
compressors
Axial-flow
compressors
Positive displacement
machine
Turbo compressors
____
Compression Volume Conversion of kinetic energy
Motion Reciprocating Rotating Rotating
Delivery Intermittent Quasi-continuous Continuous
Volume flow Low Low Low/medium Low/high Very high
Compression
ration
High Medium Medium Low
Operation Constant volume - Variable pressure Variable volume - Quasi constant pressure
Principle
Function of a
a compressor
To render a specific volume of gas from a given initial condition into a desired final condition (pressure/temperature)
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Flow path
Discharge
Diffusers
Suction
Impellers
1
2
3
5
4
7
6
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The theoretical performance curve typically has a shape as
is shown in the figure below.
THEORETICALCHARACTERISTIC
DISKFRICTION&LEAKAGELOSSESFRICTIONLOSSES
SHOCKLOSSES
SHOCKLOSSES
FLOW
HEAD
SPEED = CONSTANT
Friction losses
Friction losses are the
energy losses occurring in
the various flow passages
of the stage caused by
gas friction (like pipe
losses).
Shock losses
Shock losses occur at the
impeller vanes, diffuser
vanes and return guidevanes. At high positive or
negative incidence (inlet
angle of the gas) the flow
separates from the vane
surfaces, leading to
increased losses.
Flow characteristics
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Centrifugal compression theoryEnergy transfer through impeller
U = Circumferential velocity
W = Relative velocity
C = Absolute velocity
1 = Impeller inlet
2 = Impeller outlet on outlet
Theoretical head without losses:
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Developing the compressor curve
Rc/
Pc/
Hp
Qs /Qv /Qm
Compressor
curve for a
specific speed
N1
Rprocess,1
Q1
Rc1
Rprocess,2
Q2
Rc2
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Qs, vol
Rc
maximum speed
power limit
adding control
margins
Actual available
operating zone
Developing the compressor curve
stonewall or
choke limit
minimum speed
surge limit
process limit
stable zone
of operation
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Developing the surge cycle on the compressor curve (1)
Qs, vol
HAB
C
D
Pd
Pv
Rlosses
From A to B 20 - 50 ms Drop into surge
From C to D 20 - 120 ms Jump out of surge
A-B-C-D-A 0.3 - 3 seconds Surge cycle
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Anti-surge controller
1
UIC
VSDS
Compressor
1
FT
1
PsT
1
PdT
DischargeSuction
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Compressor performance control
PT
1
PIC
1
Process
Also called:
Throughput control
Capacity control
Process control
Matches the compressor throughput to the load
Can be based on controlling:
Discharge pressure
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Compressor performance control
PT
1
PIC
1
Process
Also called:
Throughput control
Capacity control
Process control
Matches the compressor throughput to the load
Can be based on controlling:
Discharge pressure
Suction pressure
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Compressor basics
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Compressor performance control
PT
1
PIC
1
Process
Also called:
Throughput control
Capacity control
Process control
Matches the compressor throughput to the load
Can be based on controlling:
Discharge pressure
Suction pressure Net flow to the user
Blow off
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Compressor performance control
PT
1
PIC
1
Process
Also called:
Throughput control
Capacity control
Process control
Matches the compressor throughput to the load
Can be based on controlling:
Discharge pressure
Suction pressure Net flow to the user
Blow off
Recycle
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Compressor basics
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Compressor performance control
PT
1
PIC
1
Process
Also called:
Throughput control
Capacity control
Process control
Matches the compressor throughput to the load
Can be based on controlling:
Discharge pressure
Suction pressure Net flow to the user
Blow off
Recycle
Guide vanes
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Compressor basics
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Compressor performance control
PT
1
PIC
1
Process
SIC
1
Also called:
Throughput control
Capacity control
Process control
Matches the compressor throughput to the load
Can be based on controlling:
Discharge pressure
Suction pressure Net flow to the user
Blow off
Recycle
Guide vanes
Speed
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Compressor basics
Siemens AG 2007 All rights reservedPage 17 Mass Flow
Disch.
Press
P2 Throttling
P1 Throttling
Design Point
Recycle
Control
Speed
control